well, the problem is that once they get into power they're completely moribund and start collapsing into factions. At least the LDP are united in the sheer determination to protect established interests. (I think the LDP are closest you will come to an undiluted small-"c" conservative party)
Weirdly enough - seeing as how terrible the DJP did last time - they aren't in a terrible place. They've jettisoned jokers and ill-placed wings. Ozawa's revolt failed. The JIP and PFG aren't going to destroy them - they haven't lost their status as the dominant opposition party. All they need now is some, err, policies.
But, this characterisation of the LDP is very 1990s. It pre-dates the rise of the moderate hawks (Koizumi/Abe) which have plenty of objections to the historic course of the LDP.
The Japan Socialists were both a dominant opposition and had plenty of policies - and opposition they remained. Their problem was being too extreme, but the DPJ's current problem is that too few voters trust them.